1. Field of the Invention
The present invention relates to a case and an electric motor which is used to rotate a blower fan in an air conditioner for an automobile for carrying out cooling and heating in a passenger room of the automobile, for example, and a method for producing the electric motor.
2. Description of the Prior Art
In general, there is known a case having an outer cylindrical member and an inner cylindrical member fitted in the outer cylindrical member.
A lock means is required to lock the inner and outer cylindrical members. Conventionally, the lock means is complicate in structure and an operation for locking is not easy.
On the other hand, there is known an electric motor 1 as shown in FIG. 17 (see, for example, Japanese Patent Laid-Open No. 4-190646, pages 1 to 2, FIG. 2).
The electric motor 1 includes permanent magnets 2 for generating a magnetic flux and a cylindrical yoke 3 or a case on whose inner peripheral wall the permanent magnets 2 is held.
The yoke 3 has an inner cylindrical member or a cylindrical yoke body 4 having a bottom and an outer cylindrical member or an auxiliary yoke 5 fitted in an inner peripheral wall of the yoke body 4.
The auxiliary yoke 5 is mainly formed by a pressed-processing to have a thin wall thickness and is used to conduct an attenuation of a magnetic flux leaked from the yoke body 4.
The auxiliary yoke 5 has also at an outer peripheral wall thereof a slit 5c extending from one end, an upper end 5a to the other end, a lower end 5b to enlarge peripherally the auxiliary yoke 5, as shown in FIG. 18.
The auxiliary yoke 5 is enlarged peripherally by provision of the slit 5c and fitted on the yoke body 4 to surround it. In other words, the yoke body 4 is inserted into the auxiliary yoke 5.
In addition, the auxiliary yoke 5 is provided with slits 5d which are opened at the upper and lower ends 5a and 5b of the auxiliary yoke 5, respectively to eliminate a leaked magnetic flux in the electric motor 1.
There is also known an electric motor that a cylindrical auxiliary yoke is fixed to a cylindrical yoke body by press-fitting the yoke body into the auxiliary yoke or welding them (see, for example, Japanese Patent No. 2793653, page 4, FIG. 3).
However, in each of the aforementioned electro motors, there is a problem that a position of the auxiliary yoke is not stable by it being moving on the yoke body 4 since the auxiliary yoke 5 holds merely the yoke body 4.
Further, the position of the auxiliary yoke is not necessarily stable even though the yoke body is press-fitted in the auxiliary yoke and if the auxiliary yoke is welded to the yoke body, processes of assembling the auxiliary yoke and yoke body are increased because of addition of a welding process.
Under such circumstances, it is considered that an auxiliary yoke 7 is fixed to a yoke body 6, for example, by engagement of an engaged piece 7a provided on the auxiliary yoke 7 into an engaged opening 6a provided in the yoke body 6, as shown in FIGS. 19 and 20.
However, in the structure, there is a possibility that the engaged piece 7a slides under a pressure on the outer peripheral wall of the yoke body 6 until it reaches the engaging opening 6a to thus form a scratch on the peripheral wall of the yoke body.